The Sema domain, a protein interacting module, of Plexin B
Plexins, which contain semaphorin domains, function as receptors of semaphorins and may be the ancestors of semaphorins. There are three members of the Plexin B subfamily, namely B1, B2 and B3. Plexins B1, B2 and B3 are receptors for Sema4D, Sema4C and Sema4G, and Sema5A, respectively. The activation of plexin B1 by Sema4D produces an acute collapse of axonal growth cones in hippocampal and retinal neurons over the early stages of neurite outgrowth and promotes branching and complexity. By signaling the effect of Sema4C and Sema4G, the plexin B2 receptor is critically involved in neural tube closure and cerebellar granule cell development. Plexin B3, the receptor of Sema5A, is a highly potent stimulator of neurite outgrowth of primary murine cerebellar neurons. Plexin B3 has been linked to verbal performance and white matter volume in human brain. Small GTPases play important roles in plexin B signaling. Plexin B1 activates Rho through Rho-specific guanine nucleotide exchange factors, leading to neurite retraction. Plexin B1 possesses an intrinsic GTPase-activating protein activity for R-Ras and induces growth cone collapse through R-Ras inactivation. The Sema domain is located at the N-terminus and contains four disulfide bonds formed by eight conserved cysteine residues. It serves as a ligand-recognition and -binding module.
Jiyao W et al.(2023). "The conserved domain database in 2023.",